It is a known procedure to protect a molecule during a chemical synthesis by blocking, with appropriate protecting groups, functional groups which would otherwise be reactive, but which are not intended to react during the synthesis procedure being carried out. These protecting groups are then removed following the synthesis procedure.
This technique is particularly useful during peptide syntheses. The most commonly protected functional groups are amine, alcohol or thiol functional groups. The most commonly used protecting groups include the tert-butyloxycarbonyl group (BOC), the benzyloxycarbonyl group (Z) or, indeed, even the fluorenylmethoxycarbonyl group (FMOC).
The deprotection technique conventionally used is a lysis in acidic medium, generally in anhydrous hydrohalic medium (that is to say, with a water content which is generally less than 1%, advantageously less than 10.sup.-3 %, and preferably less than 10.sup.-4 %.
However, this technique has many disadvantages. The cleaving (deprotection) reaction is sometimes slow or requires a large excess of reagent. The alkoxy groups that result have a tendency to be converted into carbocations, leading to formation of double bonds where possible, or alkylation reactions on the nucleus, which is a particular nuisance in the case of peptide syntheses in which the sequence has nucleophilic residues, such as aromatic nuclei (tryptophan, tyrosine, phenylalanine, or the like) or sulphur-containing residues (methionine).